In order to handle and connect a semiconductor die (integrated circuit device) to external systems, it is generally necessary to package the die. This usually involves mounting the die to some sort of substrate, leadframe or carrier, connecting bond pads on the die to some sort of conductive lines or traces within the package, and forming a package body around the die. The conductive lines or traces conductively exit the package body, and usually terminate in external leads, or pins or ball bumps which are suitable for connecting the packaged semiconductor die to additional elements of an electronic system.
For example, ceramic packages have a package body with a central opening (cavity) in one face for receiving the die, and lead fingers embedded in the body and extending into the opening. The die is connected (usually wire bonded) to the exposed (in the opening) portions of the lead fingers. The lead fingers are connected (internally in the package) to pins exiting a planar surface of the package. These pins are typically arranged in a rectangular (e.g., square) array. In some instances, the die-receiving cavity is "up", on one face of the package body, and the pins (e.g.) are on the other, opposite face of the package body. In other instances, the die-receiving cavity is "down", on the same face of the package as the pins (in which case there are no pins in the area of the cavity). (The pins are deemed to be on the "bottom" of the ceramic body.) In either case, the cavity is covered by a lid. In either case, an external surface of the package, when the package is mounted to a circuit board (e.g.), is visible to an observer. (Evidently, the surface of the package which is against the circuit board is not visible to an observer after the package is mounted to a circuit board.)
In another example, the die is attached and connected (usually wire bonded) to a relatively rigid (thick) lead frame having several conductive lines, and a plastic body is molded around the die and inner ends of the conductive lead frame lines. Outer ends of the lead frame lines exit the plastic body on two or four sides. Again, an external surface of the package, when mounted to a circuit board (e.g.), is visible to an observer. (Evidently, the surface of the package which is against the circuit board is not visible to an observer.)
In another example, the die is attached to a relatively flexible (thin) lead frame supported by a plastic tape, and is encapsulated in epoxy or the like. Outer ends of the lead frame lines exit the epoxy body. Both wire bonding and tape-automated bonding of the die to the lead frame lines are well known in tape packages. Typically, the die and inner portions of the tape substrate are encapsulated by a glob-top epoxy, which typically is visible to an observer when the package is mounted to a circuit board (e.g.).
Another packaging technique is mounting the die directly to a printed circuit board (PCB; also referred to as PWB, or printed wiring board) substrate. The die is connected (typically wire bonded, but may be flip-chipped) to one end of conductive traces on a face (surface) of the PCB. Typically, the die and surrounding portions of the PCB are encapsulated by a glob-top epoxy, or overmolded by plastic. In either case, a surface of the package body is visible to an observer when the package is mounted to a circuit board (e.g.).
In the assembly and subsequent inspection of semiconductor devices to circuit boards, it is essential that the proper device be mounted to the proper site on the board, and that the device is properly oriented at its location. For example, if the device is rotated 90, 180 or 270 degrees from its proper orientation it most certainly will not function as planned, since the pin-outs would be entirely wrong. To this end, certain semiconductor packages have some sort of locating/orienting feature, such as one of the corners of the package body being chamfered, an advertently missing pin, or the like. These solutions are complex, and require re-tooling to convert a non-orientation-sensitive package design to an orientation-sensitive package design. Further, semiconductor devices having different functionality may be packaged with the same package, appearing indistinguishable to an observer. Evidently, inserting the "wrong" device into a circuit board will produce inapposite results.
In some cases, different "grades" of the same device are available from a manufacturer, and the different grades may have the same visual appearance as one another. This necessitates certain inventory controls, such as labeling the trays holding the devices for shipment. Should the label come off of the tray, it may not be evident what grade of device is contained in the tray. Examples of functionality differences or different grades of the same device include radiation-hardened devices versus non-radiation-hardened, source of manufacture or distribution, various speed ratings, optionally available functions, as well as "lots" of devices that have been 100% inspected versus lots that have only been fractionally sampled. (It is also possible that the labels are or become illegible, or simply cannot be read by the user.)
What is needed is a technique for applying indicia to a semiconductor package that determines its "correct" orientation, and that differentiates the device from other, similarly-packaged devices.
It is generally well known that an operating semiconductor die will generate heat, and that it is generally beneficial to provide a heat sink, or the like, to dispose of such heat. It is also generally well known that different areas (i.e., types of circuits) on the die will generate different amounts of heat when the die is operating (e.g., based on power consumption by a circuit, speed of the circuit, etc.).
What is needed is a packaging technique that in and of itself, without the benefit of a separate heat sink, can dissipate heat in a manner superior to certain "plain" colored packages (e.g., white).
What is also needed is a packaging technique that can accommodate the different amounts of heat generated by corresponding different areas of the die operating within the package.